2:50 PM - 3:05 PM
[BGM02-05] Microbial communities in permeable sandstone in deep terrestrial subsurface
Keywords:deep biosphere, aseptic and deoxygenated drilling, microbial community analysis
Subsurface microorganisms thriving in permeable sandstone are largely unknown due to microbiological contamination with drilling fluid. To minimize contamination, drilling fluid was filter-sterilized and then injected into a borehole to obtain cores from 250-352 m deep sedimentary rocks associated with a 300-310-m deep permeable sandstone layer. Microscopic cell observations of drilling fluid samples collected from the borehole bottom after drilling 250-m deep siltstone and 303-m deep sandstone clarified that the cell density was below a detection limit (<2.2×102 cells/L). This result indicates that microbial contamination from the drilling fluid was minimized by this drilling procedure. qPCR analysis of 16S rRNA gene sequences showed the 250-m deep core sample was below a detection limit (< 2.0×105copies/ wet g), whereas the 303-m deep core sample showed an apparently high copy number (4.8×105 copies/ wet g). 16S rRNA gene amplicon analysis of the 303-m deep core sample revealed the β-proteobacterial dominance represented by high proportions of the genera Acidovorax and Aquabacterium. Catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) confirmed the β-proteobacterial dominance. Most members of the genera Acidovorax and Aquabacterium are nitrate-reducers, which is consistent with the pore-water enrichment of nitrate and nitrite in the 303-m deep permeable layer. Thus, it is concluded that these microbial properties are indigenous rather than being resulted from drilling fluid contamination and subsequent on-site and laboratory manipulations.